The present application is an exploratory R21 grant application in response to NIH Exploratory/ Developmental Research Grant Program (Parent R21): PA-09-164. The goals of the present exploratory application are to assess migration, engraftment and differentiation of cells derived from induced pluripotent stem cells (iPSC) into skeletal tissues following systemic transplantation. The ability of progenitors to migrate to skeletal tissues following systemic injection is critical for the treatment of generalized skeletal diseases. Studies in animal models assessing transplantability of MSCs to treat osteogenesis imperfecta have generated mixed results. Most of the controversies in the application of MSCs to treat OI may be due to the types of cells used for transplantation by different investigators. Embryonic stem cells (ESC) derived from the inner cell mass of the blastocyst can give rise to any cell type of the body and can be expanded indefinitely without losing their pluripotency, thus these possess a greater potential for application in cell therapies for various diseases including generalized skeletal diseases. Because of ethical concerns however, little progress has been made in harnessing the power of these cells. Recently, it has been demonstrated that mouse and human fibroblasts can be reprogrammed into an ESC-like state by introducing combinations of four transcription factors;Oct-3/4, Sox2, c-Myc and Klf4. The reprogrammed cells referred to as induced pluripotent stem cells (iPSC) offer opportunities for generating patient specific stem cells for therapeutic purposes and drug screening. As a prelude to understanding the future application of iPSC for generalized skeletal disease treatment, the present exploratory application proposes to assess migration, engraftment and differentiation of MSCs derived from iPSC following transplantation into a mouse model of osteogenesis imperfecta. The following aims will be employed to achieve the above tasks;1) generate MSCs from iPSC created by reprogramming mouse tail tip fibroblasts 2) Assess transplantability, migration, engraftment and differentiation of MSC like cells derived from iPSCs into the skeletal tissues of a mouse model of OI. Preliminary data show that we can generate iPSC by reprogramming murine tail tip fibroblasts and that the cells exhibit ESC like state. We will breed heterozygous mice that carry a collagen mutation to generate 3 mice genotypes (wildtype, heterozygous and homozygous). Fibroblasts for reprogramming will be prepared from wildtype mice and the syngeneic heterozygous and homozygous mice will be the cell recipients. Preliminary data indicate that brief exposure of iPSC to TGF-21 generates cells that exhibit MSCs characteristics. We will use this approach to generate cells for transplantation. Migration, engraftment and differentiation of the cells in vivo will be assessed by bioimaging, histology and gene expression analysis. The results from this exploratory application will provide a platform for future investigations in the application of iPSC cells for musculoskeletal tissue repair and regeneration. PUBLIC HEALTH RELEVANCE: The goals of the present exploratory application are to assess migration, engraftment and differentiation of cells derived from induced pluripotent stem cells (iPSC) into skeletal tissues following systemic transplantation. The results from this exploratory application will provide a platform for future investigations of iPSC cells in musculoskeletal tissue repair and regeneration